Did you know that cars have to be driven for five kilometres before they are functioning efficiently?   It’s much better if you can walk or cycle to places near you, like the shops or school. It’s fun too, especially if you meet some friends on the way. If you have bike panniers, a carrier or a bike basket it is easy to carry things you’ve bought so you don’t need your parents to pick you up. If you need to go further afield, take a bus or train.       Cars are bad because they pollute the atmosphere. Most cars are fuelled by petrol or diesel, though some novel fuels are being introduced.     Some people say that diesel cars pollute less, but this is only the case if the cars are regularly serviced and tuned. In general, the larger the car, the more petrol it consumes. Also, newer cars tend to be more efficient than older ones. If your family has a car, make sure they know how much fuel it uses. If it uses too much, buying new parts or tuning the car can make a difference. Another reason to try to avoid using cars is because the fumes from them contribute to the greenhouse effect. This causes an overall increase in temperature all over the world as well as an increased likelihood of extreme weather conditions such as storms. Global warming can also have an effect on plants and animals because, for instance, rivers may become too hot for the wildlife that lives there.